1. Technical Field of the Invention
The present invention relates generally to activating an occupant restraint device of a vehicle, and more specifically, to an apparatus and method for determining an anticipated rollover of the vehicle to activate the occupant restraint device of the vehicle.
2. Description of the Related Art
Methods for detecting a roll condition of a vehicle which is indicative of an upcoming rollover of the vehicle have so far been proposed. For example, Japanese Patent Application Laid-Open No. 2001-260780 discloses a method of determining an anticipated rollover of a vehicle.
According to the method, a threshold line is set on a two-dimensional map which uses the roll angle and roll angular rate of the vehicle as parameters, and an anticipated rollover of the vehicle is determined when a history line of the actual roll angle and roll angular rate of the vehicle crosses the threshold line from a non-rollover region to a rollover region, and the results of the determination are then provided to the deployment control of one or more occupant restraint devices of the vehicle such as an air curtain, a side airbag.
There are several patterns of vehicle rollover. Among them, a “curbstone trip-over” is a vehicle rollover which occurs when a vehicle sideslips, and the wheels of either the left or right side of the vehicle collide against curbstones or like obstacles, causing the vehicle to roll over about the collided wheels. Regarding the fact that a lateral (i.e., side-to-side) slip speed of a vehicle prior to collision is high in a curbstone trip-over event, the above-mentioned method adjusts the threshold line to be moved toward the original point of the map in response to the increase of the lateral slip speed of the vehicle to determine an anticipated rollover of the vehicle earlier.
However, the way of adjusting the threshold line may not be suitable for other patterns of vehicle rollover, such as “fall-over”. A fall-over is a vehicle rollover which occurs when a vehicle sideslips, and the wheels of either the left or right side of the vehicle slip off a road shoulder, causing the vehicle to roll over. In a fall-over event, even where the lateral slip speed of a vehicle prior to rollover is high, it may be more appropriate to deploy occupant restraint devices of the vehicle such as an air curtain after the roll angle of the vehicle has increased to a certain level of magnitude, so that the occupants of the vehicle are more safely protected from ejection from the vehicle.
Despite the existence of dissimilar patterns of vehicle rollover, the above-mentioned method activates the occupant restraint devices of the vehicle without an accurate recognition of the pattern of an anticipated rollover of the vehicle.